In present-day merchandising point-of-sale operations, data pertaining to the purchase of a merchandised item is obtained by reading data encoded indicia such as a bar code printed on the merchandised item. In order to standardize the bar codes used in various point-of-sale readout systems, the grocery industry has adopted a uniform product code (UPC) which is in the form of a bar code. Various reading systems have been constructed to read this bar code, including hand-held wands which are moved across the bar code and stationary optical reader systems normally located within the check-out counter and in which the bar code is read when a purchased merchandise item is moved across a window constituting the scanning area of the counter, which movement is a part of the process of loading the item in a baggage cart.
Various scanning systems presently available utilize a rotating mirror for generating a scan pattern used for reading the bar codes. Other systems utilize holograms for generating a scanning pattern on a target area through which the object bearing a bar code indicia passes. The light reflected from the bar code indicia is used in reading the bar code. An example of this type of scanning system may be found in U.S. Pat. No. 4,224,509, issued in the name of C. C. K. Cheng, which is assigned to the assignee of the present application. In this patent, a rotating disc supports a plurality of holograms, each of which produces a scanning line on a target area off-set to the lines generated by the other holograms, thereby producing a wide scanning area through which the object bearing a UPC coded label passes. Another example of a holographic scanning system is found in U.S. Pat. No. 4,113,343, in which a moving hologram generates a locus of points from a stationary light beam on a target area with the same hologram collecting the light being reflected from the document at each of the locus points and focuses this energy onto a stationary detector to provide electrical signals corresponding to the information scanned on a document.
In all of the prior art patents, the projected scan beams are all focused in a single plane which is located in the plane of movement of the object bearing the coded label. Since many mechandise items support the coded label at various angles to the focal plane of the scanning hologram, complex and expensive optical reflecting systems have been developed to transmit the scanning beam at different angles to cover all possible orientations of the label to ensure a valid scan operation. This requirement limits the operating efficiency of such scanning systems, while increasing their cost. It is therefore an object of this invention to provide an improved scanning system for projecting a multiple-line scan pattern in a bar code reader which provides an enhanced depth of focus at the target area and thus allowing the reading of a label on an object to take place irrespective of the orientation and position of the label. It is a further object of this invention to provide a scanning system which is high in reading efficiency, while low in cost.